3 Growth Factors ... Of vista — Suppose some sight in arriere, through the formative chaos, presuming the growth, fulness, life, now attain’d on the journey; (But I see the road continued, and the journey ever continued;) — Of what was once lacking on earth, and in due time has become supplied ... (Thoughts, 1855, Walt Whitman [1819–1892]) Any cell needs extracellular signals for its growth, proliferation, and survival, among other events. Chemical, mechanical, electrical, and other physical in- teractions of cells with the extracellular matrix yield functional and structural signals for normal cellular activity as well as formation and maintenance of three-dimensional tissues. Environmental chemical signals are transmitted by hormones (Sect. 1.4) and growth factors (Table 3.1), in addition to nervous cues (Sect. 1.1). In the sustained absence of growth factors, cells can undergo apoptosis (Chap. 4). Growth factor withdrawal causes loss in plasmalemmal transporters for nutrients and receptors for extracellular molecules, such as glucose, amino acids, low-density lipoprotein, iron, etc. [305]. Yet, transiently, cells have a defense system against stress for survival. Many growth factors (GF) are molecules, most often proteins, but also lipids, that bind to receptors on the cell surface (Fig. 3.1;Vol.3,Chap.6. Receptors), mainly to activate cellular proliferation and/or differentiation. The terminology currently used comes from the initial discovery context. Many growth factors have a pleiotropic nature. They thus stimulate al- most every cell type, whereas others are specific to particular cell types. The growth factors have functional redundancy, but they can have distinct effects. Their production and activation depend on the balance between inhibitory and stimulatory factors as well as their transport and storage capacities. In M. Thiriet, Control of Cell Fate in the Circulatory and Ventilatory Systems, 177 BBMCVS 2, DOI 10.1007/978-1-4614-0329-6_3, © Springer Science+Business Media, LLC 2012 178 3 Growth Factors Table 3.1. Examples of growth factors that regulate development and homeostasis of blood cells and vessels (Sources: [301–304]; gCSF: granulocyte colony-stimulating factors [CSF3]; gmCSF: granulocyte–macrophage colony-stimulating factors [CSF2]; mCSF: macrophage colony-stimulating factor [CSF1]; EGF: epidermal growth fac- tor; Epo: erythropoietin; FGF: fibroblast growth factor; IGF: insulin-like growth fac- tor; PDGF: platelet-derived growth factor; TGF: transforming growth factor; TNF: tumor-necrosis factor; VEGF: vascular endothelial growth factor; Bϕ: basophil; EC: endothelial cell; Eϕ: eosinophil; FB: fibroblast; Lϕ: lymphocyte; Mϕ: macrophage; Mo: monocyte; Nϕ: neutrophil; RBC: red blood cell [erythrocyte]; SMC: smooth muscle cell; TC: thrombocyte [platelet]). Concentration gradients of growth factors are required for cell chemotaxis. Factor Sources Targets Function gCSF Mϕ,EC Nϕ Hematopoiesis gmCSF Mo, Mϕ,TLϕ,EC,FBMϕ,Nϕ, FB Immunity mCSF T Lϕ,Mϕ Mo, Mϕ Hematopoiesis EGF TC, Mo, Mϕ, FB, EC Cell division, chemotaxis, angiogenesis Epo Kidney RBC Erythropoiesis FGF1,2 Mo, EC, FB, Mϕ FB, EC, Cell division, chemotaxis, SMC angiogenesis IGF Mϕ, FB, TC FB, EC, SMC Cell division, collagen synthesis PDGF EC, SMC, Nϕ,Nϕ,Mo,Mϕ, Cell division, chemotaxis, TC, Mϕ, FB FB, EC, SMC angiogenesis, collagen synthesis, TGFα,β Mϕ,TLϕ,EC, FB,Mϕ, Chemotaxis, angiogenesis, TC, FB Mo, Lϕ, matrix production, EC, SMC healing, inhibition of inflammation TNF Mϕ,TLϕ,Nϕ Mϕ, FB Angiogenesis, inflammation VEGF Mϕ, FB, SMC EC Angiogenesis particular, cell growth is controlled by a balance between growth-promoting and -inhibiting factors. Growth factors promote not only cell division, maturation, and function- ing, but also tissue growth and remodeling. Growth factors act on [307]: (1) growth factor-producing cells (intra- and autocrine effects),1 (2) neigh- 1 Autocrine growth factor is involved in autostimulatory growth control, in which a cell secretes a factor that binds to its receptor, which is also expressed by the 3 Growth Factors 179 GFR GPCR or RTK PIP2 Src PLC IP3 DAG Grb Sos Rac NRTK PI3K PAK PKC Ras RasGRP RacGEF JUN2K Raf Rac GTP Rac/Ras/Rho PKB JNK GAP MAP2K RhoA GTP P GEF GDP PLD Rac/Ras/Rho ERK GDI GTPase−−GDI Figure 3.1. The growth factor receptor and biochemical cascades (Source: [306]). Growth factor-bound receptor (GFR) activates the adaptor GRB coupled to the guanine nucleotide (GDP-to-GTP)-exchange factor (GEF) SOS (GRB–SOS com- plex), and subsequently Ras GTPase, Raf kinase, and mitogen-activated pro- tein kinase kinase (MAP2K) successively, and then extracellular regulated kinase (ERK) on the one hand (MAPK module), and small GTPases Rac and RhoA, and phospholipase-D (PLD) on the other hand. Ligand-bound receptors also acti- vate among other pathways: (1) phosphatidylinositol 3-kinase (PI3K) and protein kinase-B (PKB), (2) Src kinase, (3) Rac GTPase and Jun N-terminal kinase (JNK), and (4) phospholipase-C (PLC). (Lower right corner) Activation–inactivation cy- cle of small, monomeric guanosine triphosphatases (GTPase; e.g., Rac, Ras, and Rho; GTPaseGTP,GTPaseGDP: active and inactive forms) by GEF and GTPase- activating protein (GAP) and sequestration by guanine nucleotide-dissociation in- hibitors (GDI). boring cells (paracrine effect),2 (3) connecting cells (juxtacrine effect), and (4) distant cells after blood transport (endocrine effect). The set of growth factors includes cytokines and chemokines (chemotactic cytokines). Cytokines,3 or immunocytokines, are growth factors that modulate producing cell. This autogenous loop creates a substance that acts back on the cells that produce it. 2 Paracrine growth factor influences the growth and functional activities of sur- rounding cells expressing the corresponding receptor. Paracrine growth factors modulate the microenvironment. In particular, they are involved in angiogene- sis, stroma formation, modulation of immune response, activation of proteolytic enzymes, etc. 3 κυτoς: hollow object [organ] and also [like Latin cutis] envelope [by extension cell]; κιν ω:tomove. 180 3 Growth Factors activities of immunocytes. These immunomodulators, or immunotransmitters, are secreted primarily by leukocytes, either by lymphocytes (lymphokines) or monocytes and macrophages (monokines). Hence, cytokines are separated from other regulatory peptides that modulate the proliferation and activities of non-immunocytes. However, some cytokines are produced by almost the entire cell spectrum.4 Cytokines stimulate both the humoral (antibody) and cellular immune responses. Among lymphokines, interleukins (IL) are growth factors targeted to hematopoietic cells. Interferons (Ifn) are glycoproteic cytokines produced by cells of the immune system in response to foreign agents (viruses, bacteria, parasites, tumor cells). immunocytes have reciprocal activations.5 Organ development is controlled by a set of growth factors and their regula- tors (e.g., Notch). Vascular endothelial growth factor-A is the most important agent required for vasculogenesis (migration and differentiation of angioblasts and formation of primitive vascular structures), as well as angiogenesis before and after birth and vessel remodeling (Vol. 5 – Chap. 10. Vasculature Growth). Growth factors yield cell response using several regulated mechanisms, the so- called signaling pathways (Vol. 3 – Chap. 1. Signal Transduction) that lead up to substance release as well as gene expression and production of alternatively spliced variants (Vol. 1 – Chap. 5. Protein Synthesis). 3.1 Connective Tissue Growth Factor Connective tissue growth factor (CTGF)6 is a member of the CCN gene family that is activated by several factors such as transforming growth factor-β. The CCN family comprises 6 known members [308]: cysteine-rich protein- 61 (CyR61 or CCN1), connective tissue growth factor (CTGF or CCN2), nephroblastoma overexpressed protein (NOv or CCN3), and Wnt-induced se- creted protein-1 (WISP1 or CCN4), -2 (WISP2 or CCN5), and -3 (WISP3 or CCN6; Table 3.2).7 These proteins regulate cell survival, differentiation, proliferation, adhesion, and migration, as well as extracellular matrix produc- tion. Therefore, members of the CCN family are involved in implantation, 4 Heart expresses cytokines, particularly tumor-necrosis factors TNFα and -β, interleukin-1α and -1β, -2 to -6, and -10, as well as interferon-γ. 5 T lymphocytes synthesize lymphokines (gmCSF, IL3, and Ifn) that stimulate macrophages. Afterward, macrophages produce monokines (IL1) that activate T lymphocytes. 6 A.k.a. hypertrophic chondrocyte-specific protein HCS24, CCN family member CCN2, and insulin-like growth factor-binding protein IBP8 and IGFBP8. 7 Alias CCN comes from the first 3 members of the family CyR61, CTGF, and NOv. These multimodular proteins contain an insulin-like growth factor (IGF)- binding (module 1), a von Willebrand type-C (module 2), a thrombospondin-1 domain (module 3), and a C-terminus (module 4) [308]. 3.1 Connective Tissue Growth Factor 181 Table 3.2. Members of the CCN family (Source: [309]; CEF: chicken embryo fi- broblast; CTGF: connective tissue growth factor; CTGFL: connective tissue growth factor-like protein; CyR: cysteine-rich protein; ELM: expressed low in metastasis; FISP: fibroblast-inducible secreted protein; HCS: hypertrophic chondrocyte-specific gene product; HICP: heparin-inducible CCN-like protein; IGFBP: insulin-like growth factor-binding protein; IGFBPRP: IGFBP-related protein; NOv: nephrob- lastoma overexpressed protein: WISP: Wnt-inducible signaling